[SR-Users] Handling RFC3578 (Overlap Dialing) in Kamailio/ Asynchronious transaction handling

Alex Balashov abalashov at evaristesys.com
Tue Feb 4 18:58:34 CET 2014


On 02/04/2014 12:54 PM, Olle E. Johansson wrote:

> And you assume a lot of things - that your invites are sent to the same
> server, which may not be the case. DNS lookups and load balancing/failover
> is done on a per transaction basis.

In fairness, RFC 3578 does offer a fair bit of commentary on this caveat:

    However, having subsequent INVITEs routed in different ways brings
    some problems as well.  The first INVITE, for instance, might be
    routed to a particular gateway, and a subsequent INVITE, to another.
    The result is that both gateways generate an IAM.  Since one of the
    IAMs (or both) has an incomplete number, it would fail, having
    already consumed PSTN resources.

    [...]

    Routing in SIP can be controlled by the administrator of the network.
    Therefore, a gateway can be configured to generate SIP overlap
    signalling in the way described below only if the SIP routing
    infrastructure ensures that INVITEs will only reach one gateway.
    When the routing infrastructure is not under the control of the
    administrator of the gateway, the procedures of Section 2 have to be
    used instead.

And, while I agree that this is ridiculous and is in conflict with the 
basic spirit of SIP, somehow 3578 did become an RFC... I am as puzzled 
by that as you may be.  :-)

-- Alex

-- 
Alex Balashov - Principal
Evariste Systems LLC
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